递归(深度遍历dfs)
时间复杂度:O(n),遍历二叉树每个结点
空间复杂度:O(n),递归栈深度就是二叉树的高度,其中最坏情况是二叉树退化为链表,深度最大为n
/*
struct TreeNode {
int val;
struct TreeNode *left;
struct TreeNode *right;
TreeNode(int x) :
val(x), left(NULL), right(NULL) {
}
};*/
class Solution {
public:
int TreeDepth(TreeNode* pRoot) {
if(pRoot==nullptr) return 0;
int lDepth = TreeDepth(pRoot->left);
int rightDepth = TreeDepth(pRoot->right);
return max(lDepth, rightDepth) + 1;
}
};
或
class Solution {
public:
int TreeDepth(TreeNode* pRoot) {
if(pRoot==nullptr) return 0;
return max(TreeDepth(pRoot->left), TreeDepth(pRoot->right)) + 1;
}
};
层次遍历(dfs)
时间复杂度:O(n),遍历二叉树每个结点
空间复杂度:O(n),辅助队列的最大长度不会超过n
class Solution {
public:
int TreeDepth(TreeNode* pRoot) {
if(pRoot==nullptr) return 0;
queue<TreeNode*> q;
q.push(pRoot);
int level = 0;
while(!q.empty()){
int size = q.size();
while(size--){
auto node = q.front();
q.pop();
if(node->left) q.push(node->left);
if(node->right) q.push(node->right);
}
level++;
}
return level;
}
};
class Solution {
public:
int TreeDepth(TreeNode* pRoot) {
if(pRoot==nullptr) return 0; //空结点没有深度
queue<TreeNode*> q; // 生成队列
q.push(pRoot); //根入队
int level = 0; //记录深度
while(!q.empty()){ // bfs
int size = q.size(); //记录当前层有多少结点
for (int i=0; i<size; i++) {
auto node = q.front(); // TreeNode* node = q.front();
q.pop();
if(node->left) q.push(node->left);
if(node->right) q.push(node->right);
}
level++; // 每访问完一层结点,深度加1
}
return level;
}
};